Structural and electronic properties of doped oligothiophenes in the presence of p‑toluenesulfonate acids

We investigate the geometric and electronic structure of singly oxidized oligothiophenes in the presence of the counterion named p-toluenesulfonate acid (p-TSA) by performing ab initio density functional theory calcula- tions using Becke-Half-and-Half-Lee-Yang-and-Parr hybrid functional on chains of up to 12 thiophene rings. Different possibilities of positioning the counterion along the con- jugated chain are studied. The calculations indicate that the side orientation is the most stable structure of pTh/p- TSA complex. Further, the influence of the counterion on the charge distribution and structural geometry of charged oligothiophenes is also investigated. In the last part of the work, the solid-state packing effects are considered by stud- ying the stacking of two conjugated chains in the presence of two counterions. Our results are consistent with several experimental observations on similar conjugated polymers.